Set default append location?
It's possible to let it start in a certain directory from script:
bpy.ops.wm.link_append('INVOKE_AREA', directory="C:\\tmp")

Hence, it's possible to bind a key combination for that as well. You can simply edit the existing Shift+F1 binding:



Set search type to Key-Binding, search for "Shift F1", expand the entry and pick a directory.